Differentiating focal autoimmune pancreatitis and pancreatic ductal adenocarcinoma: contrast-enhanced MRI with special emphasis on the arterial phase.

• Diagnosis of focal-type AIP vs. PDA using imaging techniques is extremely challenging. • Lesion contrast in the arterial-phase MRI differs significantly between focal-type AIP and PDA. • Quantitative analysis of lesion contrast using CE-MRI, particularly at the arterial phase, is helpful to differentiate focal-type AIP from PDA.